A 2nd Lieutenant in US Armed Forces, specifically the Marine Corps. "Butterbar", a reference to the gold bar rank insignia worn on the uniform, is a term generally used in a condescending or patronizing manner towards a boot lieutanant that thinks he knows everything, yet couldn't lead the way out of his own ass with a map and flashlight.

After completing OCS (Officer Candidate School) and TBS (The Basic School) a large number of newly mintedbutter bars tend to think that they are Chesty Puller and General Patton reincarnated and have the belief that after months of schooling they know much more than enlisted Marines that have been doing the job much longer.

Some have been so stupid as to actually stop a Gunner (THE Man in the USMC) or a Sergeant Major and demand a salute. Several pounds of flesh and ego are stripped before the Lt. knows what is happening and before you know it he's standing locked at point of attention like a fatbody at chowtime.

After several years of seasoning, and realizing that PT studliness doesn't make them a great leader, the butter bar becomes a 1st. Lt. and usually has a clue by then.

Phrases often heard from a Butterbar:

"In my experience..."

"It would behoove you..." (an attempt to sound salty or like a senior enlisted)

"We need to execute gents. We need to execute or we'll be in a $hit sandwich" (repeats every chances he gets, simply because he likes the way it sounds.)